The (im)possibility of strong chemical tagging

TL;DR

This study assesses the feasibility of strong chemical tagging to identify dispersed co-natal stars in the Galactic disc, finding significant overlaps in chemical signatures that limit its effectiveness.

Contribution

It provides a comprehensive analysis using high-resolution data and clustering techniques, demonstrating the limitations of chemical tagging in reconstructing star formation history.

Findings

Only 9 out of 31 clusters recovered at 40% homogeneity

Over 70% of identified groups are statistical, not real clusters

Chemical signatures overlap significantly among different clusters

Abstract

The possibility of identifying co-natal stars that have dispersed into the Galactic disc based on chemistry only is called strong chemical tagging. Its feasibility has been debated for a long time, with the promise of reconstructing the detailed star-formation history of a large fraction of stars in the Galactic disc. We investigate the feasibility of strong chemical tagging using known member stars of open clusters. We analysed the largest sample of cluster members that have been homogeneously characterised with high-resolution differential abundances for 16 different elements. We also investigated the possibility of finding the known clusters in the APOGEE DR16 red clump sample with 18 chemical species. For both purposes, we used a clustering algorithm and an unsupervised dimensionality reduction technique to blindly search for groups of stars in chemical space. Even if the internal coherence of the stellar abundances in the same cluster is high, typically 0.03 dex, the overlap in the chemical signatures of the clusters is large. In the sample with the highest precision and no field stars, we only recover 9 out of the 31 analysed clusters at a 40% threshold of homogeneity and precision. This ratio slightly increases when we only use clusters with 7 or more members. In the APOGEE sample, field stars are present along with four populated clusters. In this case, only one of the open clusters was moderately recovered. In our best-case scenario, more than 70% of the groups of stars are in fact statistical groups that contain stars belonging to different real clusters. This indicates that the chances of recovering the majority of birth clusters dissolved in the field are slim, even with the most advanced clustering techniques. We show that different stellar birth sites can have overlapping chemical signatures [abridged]